Hi All, 

This patch adjusts the cost model so that when both sdiv and udiv are possible
it prefers udiv over sdiv. This was done by making sdiv slightly more expensive
instead of making udiv cheaper to keep the baseline costs of a division the same
as before.

Similar to aarch64 this patch along with my other two related mid-end changes
makes a big difference in division by constants.

Given:

int f2(int x)
{
  return ((x * x) % 300) + ((x * x) / 300);
}

we now generate

f2:
	mul	r3, r0, r0
	mov	r0, r3
	ldr	r1, .L3
	umull	r2, r3, r0, r1
	lsr	r2, r3, #5
	add	r3, r2, r2, lsl #2
	rsb	r3, r3, r3, lsl #4
	sub	r0, r0, r3, lsl #2
	add	r0, r0, r2
	bx	lr

as opposed to

f2:
	mul	r3, r0, r0
	mov	r0, r3
	ldr	r3, .L4
	push	{r4, r5}
	smull	r4, r5, r0, r3
	asr	r3, r0, #31
	rsb	r3, r3, r5, asr #5
	add	r2, r3, r3, lsl #2
	rsb	r2, r2, r2, lsl #4
	sub	r0, r0, r2, lsl #2
	add	r0, r0, r3
	pop	{r4, r5}
	bx	lr

Bootstrapped and reg tested on arm-none-eabi
with no regressions.

OK for trunk?

Thanks,
Tamar


gcc/
2017-05-02  Tamar Christina  <tamar.christina@arm.com>

	* config/arm/arm.c (arm_rtx_costs_internal): Make sdiv more expensive than udiv.


gcc/testsuite/
2017-05-02  Tamar Christina  <tamar.christina@arm.com>

	* gcc.target/arm/sdiv_costs_1.c: New.